The present work involves developing a series of dextran molecules to study the permeability characteristics of a group of biological and synthetic membranes. It is expected that a molecular size ranging from 10 to 40 A will be developed. The membranes to be characterized are those currently used for treatment of kidney failure, namely, hemodialysis membrane, the peritoneal membrane, and hemofiltration membranes. At least 2 hemodialysis and 2 hemofiltration membranes will be characterized with the dextran marker solutes. A solute clearance profile (plot of clearance vs. molecular weight) will be developed for each membrane and this in turn will be contrasted with the solute clearance profile of the intact mammalian kidney. The goal will be to identify how closely the performance of the synthetic membranes matches that of the human kidney in terms of solute clearance.